The effect of sulphur dioxide exposure on indices of heart rate variability in normal and asthmatic adults

Sulphur dioxide (SO 2 ) is an important air pollutant and causes bronchoconstriction in normal and asthmatic adults. This paper has explored the autonomic consequences of SO 2 exposure using the spectral analysis of heart rate variability. Electrocardiogram recordings were made in 12 normal and 12 asthmatic adults undergoing pollutant exposures. Exposures were of a 1 h duration, double blind, in random order, ≥2 weeks apart and included air and 200 parts per billion SO 2 . Spectral analysis of R-R intervals was performed. SO 2 exposure was associated with an increase in total power (TP) and high (HF) and low frequency (LF) power in the normal subjects, and a reduction in these indices in the subjects with asthma. The difference in TP with SO 2 exposure compared to air was +1730 ms 2 in the normal group and −1021 ms 2 asthmatic group (p<0.003). For HF the respective values were +964 ms 2 and −539 ms 2 (p=0.02) and for LF, +43 7 ms 2 and −57 2 ms 2 (p=0.01). No change in lung function or symptoms was observed in either group. This suggests that SO 2 exposure at concentrations which are frequently encountered during air pollution episodes can influence the autonomic nervous system. This may be important in understanding the mechanisms involved in SO 2 induced bronchoconstriction, and of the cardiovascular effects of air pollution.